linux-kernel - Re: [PATCH 1/3] tpm: Disable TCG_TPM2

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Message-Id: <D1KIFPNBNGKH.IJKFRXH8WINU@kernel.org>
Date: Mon, 27 May 2024 17:51:58 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Vitor Soares" <ivitro@...il.com>, "James Bottomley"
 <James.Bottomley@...senPartnership.com>, <linux-integrity@...r.kernel.org>
Cc: <keyrings@...r.kernel.org>, "Peter Huewe" <peterhuewe@....de>, "Jason
 Gunthorpe" <jgg@...pe.ca>, "Mimi Zohar" <zohar@...ux.ibm.com>, "David
 Howells" <dhowells@...hat.com>, "Paul Moore" <paul@...l-moore.com>, "James
 Morris" <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 <linux-kernel@...r.kernel.org>, <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 1/3] tpm: Disable TCG_TPM2_HMAC by default

On Thu May 23, 2024 at 10:59 AM EEST, Vitor Soares wrote:
> On Wed, 2024-05-22 at 19:11 +0300, Jarkko Sakkinen wrote:
> > On Wed May 22, 2024 at 5:58 PM EEST, Vitor Soares wrote:
> > > I did run with ftrace, but need some more time to go through it.
> > > 
> > > Here the step I did:
> > > kernel config:
> > >   CONFIG_FUNCTION_TRACER
> > >   CONFIG_FUNCTION_GRAPH_TRACER
> > > 
> > > ftrace:
> > >   # set filters
> > >   echo tpm* > set_ftrace_filter
> > > 
> > >   # set tracer
> > >   echo function_graph > current_tracer
> > > 
> > >   # take the sample
> > >   echo 1 > tracing_on; time modprobe tpm_tis_spi; echo 0 > tracing_on
> > > 
> > > regards,
> > > Vitor Soares
> > 
> > I'm now compiling distro kernel (OpenSUSE) for NUC7 with v6.10 contents.
> > 
> > After I have that setup, I'll develop a perf test either with perf or
> > bpftrace. I'll come back with the possible CONFIG_* that should be in
> > place in your kernel. Might take up until next week as I have some
> > conference stuff to prepare but I try to have stuff ready early next
> > week.
> > 
> > No need to rush with this as long as possible patches go to rc2 or rc3.
> > Let's do a proper analysis instead.
> > 
> > In the meantime you could check if you get perf and/or bpftrace to 
> > your image that use to boot up your device. Preferably both but
> > please inform about this.
> > 
>
> I already have perf running, for the bpftrace I might not be able to help.

The interesting function to look at with/without hmac is probably
tpm2_get_random().

I attached a patch that removes hmac shenigans out of tpm2_get_random()
for the sake of proper comparative testing.

BR, Jarkko

View attachment "0001-fixup.patch" of type "text/x-patch" (1663 bytes)